The present invention relates to a steering apparatus, and principally to a steering apparatus that can be used preferably as the steering apparatus of a ship.
(1) A Manual Steering Apparatus that Uses a Helm Pump
By taking reference to FIG. 28, a manual steering apparatus of the prior art using a pump that can be rotated either in forward or reverse direction and can discharge a liquid (oil) of a quantity proportional to the rotating angle (hereinafter referred to as a helm pump) will be described below with reference to FIG. 28. This apparatus has a steering wheel 13 as steering means and a hemp pump 10 provided on the steersman side and a double action cylinder mechanism provided on the rudder side of the ship as means to drive the rudder 27. The steering means and the double action cylinder mechanism are connected with a hydraulic channel 14 that consists of a pair of hydraulic circuits 14a, 14b, so as to constitute a hydraulic circuit a fully closed circuit construction as a whole.
When the steersman turns the steering wheel 13 so that a liquid is discharged from a right port 11 of the helm pump 10, for example, the liquid discharged from a right port 11 of the helm pump 10 enters a right chamber 25 of a cylinder through the hydraulic circuit 14a and a right port 23 of a double action cylinder 20, so as to push a piston 21 to move in a direction depicted as leftward in the drawing. This causes the rudder 27 to be steered via a piston rod 22, thereby effecting the steering operation.
When the piston 21 is pressed to move to the left in the double action cylinder 20, accordingly the liquid contained in the left chamber 26 of the cylinder is forced through the left port 24 into the hydraulic circuit 14b, so that the liquid in the hydraulic circuit 14b passages through the left port 12 of the helm pump 10 and enters the helm pump 10. The amount of liquid that enters the helm pump 10 is equal to the amount of the liquid that has been discharged.
When the steering wheel 13 is turned in a direction opposite to the above, the liquid flows in a direction opposite to the above thereby to achieve an effect opposite to that described above.
In the manual steering apparatus using the helm pump 10, a proportional relationship is maintained between the rotating angle of the steering wheel 13 and the moving distance of the piston rod 22, so that the rotating angle of the steering wheel 13 and the position of the rudder 27 have a particular relation with each other. As a result, the rudder can be steered by turning the steering wheel 13 over a certain angle thereby to turn the rudder 27 to a required angle.
In the case described above, the rudder 27 is caused to move at a speed proportional to the rotating speed of the steering wheel 13.
However, the manual steering apparatus requires it to rotate the steering wheel 13 manually against the resistance of the rudder 27. This is not a problem in a small vessel where the rudder 27 poses a relatively small resistive force, although a significant magnitude of force is required to operate the steering wheel 13 in a large vessel where the rudder 27 poses a large resistive force.
(2) A Power-Assisted Steering Apparatus of the Prior Art Using a Metering Device
For the purpose of solving the problem of the manual steering apparatus described above, power-assisted steering apparatuses have been provided that reduce the amount of force required when steering. A latest example of the power-assisted steering apparatus will be described below with reference to FIG. 29 through FIG. 31.
FIG. 29 shows a rotary switching valve 130 placed at a neutral position (a position where the rudder is not effective). FIG. 30 shows the rotary switching valve 130 shifted to the left so that a piston rod 22 is moved to the right by hydraulic pressure. FIG. 31 shows the rotary switching valve 130 shifted to the right so that a piston rod 22 is moved to the left by hydraulic pressure. In the description that follows, the rudder 27 linked to the piston rod 22 is omitted.
The power-assisted steering apparatus comprises a mechanism that consists of a metering device 100, a hydraulic pump 120 that supplies the liquid and has a tank 110 for holding returned excess liquid, etc.
While making reference to FIG. 30, too, operation and construction of the apparatus will be described below.
When the steering wheel 103 is turned away from the neutral position in one direction, a rotary switching valve 130 that is mechanically linked with the steering wheel 103 so as to operate as the steering wheel 103 rotates moves from the state shown in FIG. 29 to the left into the state shown in FIG. 30. Under this condition, a pressure switch 123 is turned on by an increasing pressure of the liquid discharged from the metering pump 100, so that a pump motor 121 that is mechanically linked with the hydraulic pump 120 is started to run. The liquid discharged from a lower port 120b of the hydraulic pump 120 flows through a port 132b and a port 132c of a rotary switching valve right chamber 132 and enters a right-hand port 101 of the metering device 100. The amount of liquid that enters is limited to the measured quantity that is determined by the rotating speed of the steering wheel 103. Excess of the liquid passes through a right-hand bypass passage 132g provided in the rotary switching valve 130 and returns to the tank 110 via a port 132a of the rotary switching valve right chamber 132. The liquid introduced into the metering device 100 is discharged through the left-hand port 102 of the metering device to be circulated through a port 132d and a port 132f of the rotary switching valve right chamber 132 of the rotary switching valve 130 and the left-hand port 24 of the cylinder 20 thereby to enter the left-hand chamber 25 of the cylinder so as to drive the piston 21 and the piston rod 22. The liquid emerging from the cylinder right-hand chamber 25 passes through a port 132e and then a port 132a of the rotary switching valve right chamber 132 of the rotary switching valve 130 thereby to return to the tank 110.
In case the steering wheel 103 is turned in a direction opposite to that described above, the liquid passes through the circuit as shown in FIG. 31, so that the piston 21 and the piston rod 22 move in a direction opposite to that described above.
In the power-assisted steering apparatus of the prior art described above, the pump motor 121 rotates at a constant speed so that the hydraulic pump 120 always discharges the maximum flow rate required by the rudder 27. In case the flow rate required by the cylinder 20 is less than the maximum flow rate, excess of the liquid is all returned to the tank 110 through the right-hand bypass passage 132g or the left-hand bypass passage 133g of the rotary switching valve 130.
Therefore, the power-assisted steering apparatus of the prior art described above reduces the force required of the steersman, although the hydraulic pump 120 continues to supply the liquid unnecessarily most of the time, resulting in a significant waste of energy. It has also such a drawback as the steersman cannot get the feel of moving the rudder 27 against external force.
An object of the present invention is to provide a power-assisted steering apparatus that gets rid of the drawbacks of the power-assisted steering apparatus of the prior art described above, allows the steersman to easily operate the steering wheel and saves energy consumption with minimized waste of energy.
Another object of the present invention is to provide a power-assisted steering apparatus of better steerability that lets the steersman feel the resistive force exerted on the steering wheel from the outside as in the case of the manual steering apparatus.
In order to achieve objects described above, the steering apparatus of the present invention employs a hydraulic pump, used to reduce the force required for steering, that discharges the same amount of liquid which is discharged from a helm pump, without discharging excess liquid as in the case of the hydraulic pump used in the power-assisted steering apparatus of the prior art described above. That is, entire hydraulic circuit of the apparatus is constructed in a fully closed circuit, where the liquid of the same discharging flow rate as that of the helm pump 10 is drawn so as to increase the pressure, thereby to move the steering wheel with a cylinder driven by the increased pressure.
Since the discharging flow rate of the helm pump 10 depends on the rotating speed of the helm pump that is related to the operation of the steering wheel, a variable speed motor is used to drive the hydraulic pump of the present invention in order to accommodate changes in the liquid flow rate (a constant speed motor is used in the prior art). Specifically, either voltage or frequency of the power supply to a motor drive circuit is changed to change the motor speed.
In the apparatus of the present invention, the motor that drives the hydraulic pump is controlled by means of the resistive pressure acting on the helm pump during rotation of the helm pump 10, for example a value that is related (by proportional or other relation) to the pressure difference between the discharge side and suction side of the helm pump. The resistive force corresponds to the force (torque) required to rotate the helm pump. This means that the hydraulic pump motor is controlled in accordance to the torque of the rotating helm pump.
According to the present invention, therefore, when the steering wheel is not being operated and the helm pump it not rotating accordingly, the hydraulic pump is not driven to run, too. The hydraulic pump is driven to run only when the helm pump rotates due to the operation of the steering wheel.
Moreover, since the hydraulic pump is controlled by means of the resistive pressure generated during rotation of the helm pump (equivalent to the torque required to rotate the helm pump), energy consumption can be significantly reduced compared to the hydraulic pumping means employed in the power-assisted steering apparatus of the prior art that always causes the liquid to flow with a capacity greater than required.
Also according to the present invention, resistive force from the outside can be transmitted from the rudder via the hydraulic circuit or the helm pump to the steering wheel, so that the steersman can get the feeling of manual steering. Such a feeling of manual steering can never be experienced with the power-assisted steering apparatus of the prior art.
The steering apparatus of the present invention that is based on the basic concept and operation described above has the following features.
The steering apparatus of the present invention has the first feature that the steering apparatus comprises a steering wheel 13 and a helm pump 10 that can be rotated in both the forward and reverse directions by operating said steering wheel 13 and discharges a liquid of a quantity proportional to the rotating angle provided as steering means on the steersman side, and double action cylinder means consisting of a cylinder 20, a piston 21 and a piston rod 22 provided on rudder 27 side of the ship as means for moving the rudder 27, with the steering means and the double action cylinder means being connected with each other by means of a hydraulic circuit, so that the entire liquid that is discharged from the helm pump 10 is introduced via the hydraulic circuit into one chamber of the cylinder 20 of the double action cylinder means and the same amount of liquid is discharged from the other chamber of the cylinder 20 so as to flow through the hydraulic circuit into the helm pump 10, thus constituting the hydraulic circuit having fully closed circuit construction as a whole and moving the rudder 27 by an amount corresponding to the amount of liquid introduced into said cylinder 20,
wherein pump means that generates the discharging pressure in the same direction as the discharging direction from the helm pump 10 against the resistive pressure from the oil hydraulic circuit generated during rotation of the helm pump 10 due to the operation of said steering wheel 13 is installed in series in part of the fully closed hydraulic circuit, so that the steering resistance of the steering wheel 13 is automatically reduced by means of the assistance of said pump means.
According to the first feature described above, when the helm pump 10 is caused to rotate in one direction, forward or reverse, by the operation of the steering wheel 13 and the liquid is discharged by the helm pump 10 into the hydraulic circuit, resistive pressure from the hydraulic circuit is generated by rotation of the helm pump 10. Thus the operation of the steering wheel 13 becomes difficult when the resistive pressure of the liquid increases (this is the case of the manual steering apparatus of the prior art). According to the first feature described above, since such a constitution is employed as the pressure is generated in the same direction as the discharging direction of the helm pump 10 with the discharging pressure corresponding to the resistive pressure exerted by the pumping means installed in series in the hydraulic circuit according to the rotation of the helm pump 10, the steering resistance of the steering wheel 13 is reduced by the amount of liquid discharged by the pumping means so that steering operation becomes lighter and easier.
Since the apparatus having the first feature is constituted as the fully closed circuit as a whole, liquid of exactly the same quantity as discharged by the helm pump 10 into the hydraulic circuit is exactly introduced into the cylinder 20, thus making it possible to move the rudder 27 by an amount exactly corresponding to the amount of liquid discharged. That is, direction, speed and distance (rudder angle) of moving the rudder 27 can be exactly determined according to the direction, speed and angle of rotating the steering wheel 13.
Also because the apparatus is made in fully closed circuit construction as a whole, it is made possible to reflect the resistance to the operation of the steering wheel 13 to the resistive pressure of liquid generated in the hydraulic circuit, resistance against the steering operation can be reduced without loss of energy by generating the steering assisting pressure with the pumping means only during the period when the resistance against steering is generated and to the magnitude that corresponds to the resistance against steering.
Also in the apparatus having the first feature, the resistance which the steersman receives during the steering operation can represent, in addition to the rotating speed of the helm pump 10, the resistance against the movement of the rudder 27 exerted from the outside via the hydraulic circuit 14, and therefore the steersman can get the feeling of manual steering with the resistance against steering operation being reduced.
In addition to the constitution of the first feature described above, the steering apparatus of the present invention has a second feature that the hydraulic circuit 14 consists of a pair of hydraulic circuits 14a, 14b installed between and connecting the steering means and the double action cylinder. In such a constitution as the entire discharging flow rate of the helm pump 10 is introduced into one chamber of the cylinder 20 via one of the pair of hydraulic circuits 14a, 14b into the cylinder 20 and the same amount of liquid is discharged from the other chamber of the cylinder 20 to flow through the other one of the pair of hydraulic circuits 14a, 14b into the helm pump 10, the hydraulic circuit 14 consisting of the fully closed circuit as a whole is formed and the rudder 27 is moved over a distance that corresponds to the amount of liquid introduced into the cylinder 20.
At least a hydraulic pump 30 capable of discharging in both ways is provided as the pump means, the hydraulic pump 30 capable of discharging in both ways being installed in series in the hydraulic circuit 14b of the hydraulic circuit 14 that has the fully closed circuit construction, wherein a discharging pressure is applied in the same direction as the discharging direction of the helm pump 10 by the pump means including the hydraulic pump 30 in accordance to the resistive pressure against the operation of the steering wheel 13, so that the steering resistance of the steering wheel 13, is automatically reduced.
According to the second feature described above, the discharging flow from the helm pump 10 due to the operation of the steering wheel 13 passes through one of the pair of hydraulic circuits 14a, 14b of the hydraulic circuit 14 consisting of the fully closed circuit so that the liquid of the same amount as that discharged enters one of the chambers of the cylinder 20, thereby to push the piston 21 and move the rudder 27. Accordingly, the same amount of liquid is discharged from the other chamber of the cylinder 20 to pass the other passage of the pair of hydraulic circuits 14a, 14b and enters the helm pump 10. Meanwhile the hydraulic pump capable of discharging in both ways is provided as the pump means and is installed in series in one of the hydraulic circuits 14a, 14b. 
When a resistive pressure against the discharge pressure of the helm pump 10 is generated by operating the steering wheel 13 to rotate the helm pump 10 in either direction, the hydraulic pump 30 capable of discharging in both ways is driven to discharge the liquid at a discharging pressure corresponding to the resistive pressure in the same direction as the discharging direction of the helm pump 10. This reduces the resistance exerted on the steering wheel 13 by the amount corresponding to the liquid discharged by the pump means, thus making the steering operation easier.
Since the hydraulic pump can discharge the liquid in both ways, operation of the steering wheel 13 in both ways can be facilitated by a single pump. Since the entire apparatus is made in the fully closed circuit construction similarly to the case of the first feature, the rudder 27 can be moved by the amount that exactly corresponds to the discharging flow rate of the helm pump 10 and a resistive pressure that exactly represents the rotation and other conditions of the helm pump 10 caused by the operation of the steering wheel can be obtained. As a result, the pump means is required only to generate the minimum necessary discharging pressure. Also because the pump means is driven only during the period when the steering wheel is operated and the helm pump 10 is rotating, thus energy saving operation can be achieved.
Also the resistance which the steersman receives when operating the steering wheel 13 can represent, in addition to the rotating speed of the helm pump 10, the resistance against the movement of the rudder 27 exerted from the outside via the hydraulic circuit 14, and therefore the steersman can get the feeling of manual steering with the resistance against steering operation being reduced.
In the steering apparatus of the present invention having the constitution depicted in the second feature described above, the pump means that generates the pressure of the liquid in the same direction as the discharging direction of the helm pump 10 has a pressure detector that detects the resistive pressure generated by the rotation of the helm pump 10, and the motor drive circuit 41 of the hydraulic pump 30 is controlled so as to generate the discharging pressure that corresponds to the resistive pressure detected by the pressure detector, as the third feature.
According to the third feature, in addition to the operation and effect of the second feature, when the resistive pressure is generated against the discharge pressure of the helm pump 10 in response to the operation of the steering wheel 13, the pressure detector of the pump means detects the resistive pressure. Then the motor drive circuit of the hydraulic pump 30 is controlled in accordance to the resistive pressure detected by the pressure detector. Accordingly, the hydraulic pump 30 is driven to run with a discharge pressure corresponding to the direction and magnitude of the resistive pressure, and therefore the resistance acting on the steering wheel 13 is reduced.
According to the third feature, the steering wheel can be operated lightly and easily by controlling the hydraulic pump 30 in accordance to the resistive pressure generated by the rotation of the helm pump 10.
Other effects including the energy saving and the feeling of manual steering operation are achieved similarly to the case of the second feature.
The steering apparatus of the present invention of fourth feature has the constitution of the second feature wherein the pump means that generates the discharging pressure in the same direction as the discharging direction of the helm pump 10 has a pressure detector that detects the resistive pressure generated by the rotation of the helm pump 10 and a current detector that detects the motor current of the hydraulic pump 30, so that the resistive pressure detected by the pressure detector and the actual discharging pressure of the hydraulic pump 30 detected by the current detector are compared and the motor drive circuit 41 of the hydraulic pump 30 is controlled according to the difference.
According to the fourth feature, in addition to the operation and effect of the second feature, resistive pressure generated by rotation of the helm pump 10 is detected by the pressure detector of the pump means and the motor current of the hydraulic pump 30 during operation is detected by the current detector during operation of the steering wheel 13. Since the motor current of the hydraulic pump 30 during operation corresponds to the actual discharging pressure of the hydraulic pump 30, the value detected by the pressure detecting means and the value detected by the current detecting means can be easily compared to each other by converting the values to equivalents of the same unit. That is, the resistive pressure acting against the operation of the steering wheel 13 and the actual discharging pressure of the hydraulic pump 30 are compared so that the motor drive circuit 41 of the hydraulic pump 30 is controlled according to the difference of these values. Thus the discharging pressure of the hydraulic pump 30 is quickly corrected to a proper value so as to quickly reduce the resistive pressure acting against the operation of the steering wheel 13 and stabilization can be achieved quickly. The control according to the difference makes it possible to adjust the degree of assistance to the steering to suit the preference of the steersman.
According to the fourth feature, since the resistance against the steering operation is controlled according to the difference between the resistive pressure acting against the rotation of the helm pump 10 and the actual discharging pressure of the hydraulic pump 30, the resistive pressure against the steering operation can be reduced more quickly and stabilized at the reduced level.
Other effects including the energy saving and the feeling of manual steering operation are achieved similarly to the case of the second feature.
The steering apparatus of the present invention of fifth feature has such a constitution, in addition to the constitution of the first feature, as the hydraulic circuit 14 consists of a pair of hydraulic circuits 14a, 14b installed between and connecting the steering means and the double action cylinder means so that the entire liquid discharged from the helm pump 10 is introduced into one of the chambers of the cylinder 20 via one of the pair of hydraulic circuits 14a, 14b and the same amount of liquid is discharged from the other chamber of the cylinder 20 to flow through the other one of the pair of hydraulic circuits 14a, 14b into the helm pump 10, with the hydraulic circuit 14 being made in the construction of the fully closed circuit as a whole and the rudder 27 is moved over a distance that corresponds to the amount of liquid introduced into the cylinder 20.
At least a pair of hydraulic pumps 30, 31 capable of discharging in both ways are provided as the pump means, the pair of hydraulic pumps 30, 31 capable of discharging in both ways being installed in series in the hydraulic circuits 14a, 14b, respectively, of the hydraulic circuit 14 that is formed in the fully closed circuit, so that discharging pressure is applied in the same direction as the discharging direction of the helm pump 10 by the pump means that includes the pair of hydraulic pumps 30, 31 in accordance to the resistive pressure acting against the operation of the steering wheel 13, so that the steering resistance of the steering wheel 13 is automatically reduced.
According to the fifth feature described above, the liquid discharged from the helm pump 10 due to the operation of the steering wheel 13 passes through one of the pair of hydraulic circuits 14a, 14b of the hydraulic circuit 14 that has the fully closed circuit construction so that the liquid of the same amount as that discharged enters one of the chambers of the cylinder 20, thereby to push the piston 21 and move the rudder 27. Accordingly, the same amount of liquid is discharged from the other chamber of the cylinder 20 to pass through the other liquid passage of the pair of hydraulic circuits 14a, 14b and enters the helm pump 10.
Meanwhile a pair of hydraulic pumps capable of discharging in both ways are provided as the pump means and are installed in series in the hydraulic circuits 14a, 14b, respectively.
When a resistive pressure against the discharge pressure of the helm pump 10 is generated by operating the steering wheel 13 to turn the helm pump 10 in either direction, the pair of hydraulic pumps 30, 31 capable of discharging in both ways are driven to discharge the liquid in the same direction as the discharging direction of the helm pump at a discharging pressure that corresponds to the resistive pressure. This reduces the resistance exerted on the steering wheel 13 by the amount corresponding to the liquid discharged by the pump means, thus making the steering operation easier.
Since the hydraulic pumps 30, 31 are capable of discharging in both directions, operation of the steering wheel 13 in both ways can be facilitated by each of the pumps. Use of the pair of the hydraulic pumps 30, 31, in particular, reduces the required output of by each of the pumps 30, 31 to a half of the total output required, thus reducing the load on the pumps 30, 31. Use of the pair of the hydraulic pumps also makes the transfer of the liquid between the pair of hydraulic circuits 14a, 14b more uniform and stabilized.
Also in the event of a failure of one of the hydraulic pumps, the operation can be continued with the remaining pump that works.
Similarly to the case of the first feature, since it is required to drive the pumps 30, 31 only during the period when the steering wheel 13 is operated and resistance is generated against the steering operation, with an output that corresponds to the resistance against steering, energy saving operation can be achieved. Moreover the steersman can get the feeling of manual steering with the resistance against steering operation being reduced.
According to the sixth feature of the steering apparatus of the present invention, in addition to the constitution of the fifth feature, the pump means that generates the discharging pressure in the same direction as the discharging direction of the helm pump 10 has a pressure detector that detects the resistive pressure generated by rotation of the helm pump 10, while the motor drive circuit 41 that drives the pair of hydraulic pumps 30, 31 in common is controlled so as to generate a discharge pressure that corresponds to the resistive pressure of the liquid detected by the pressure detector.
According to the sixth feature, the steering wheel can be operated lightly and easily by controlling the hydraulic pumps 30, 31 in accordance to the resistive pressure generated by rotation of the helm pump 10.
Other effects including the energy saving and the feeling of manual steering operation are achieved similarly to the case of the fifth feature.
The steering apparatus of the present invention of seventh feature has the constitution of the fifth feature wherein the pump means that generates discharging pressure in the same direction as the discharging direction of the helm pump 10 has a pressure detector that detects the resistive pressure generated by rotation of the helm pump 10 and a current detector that detects the motor currents of the pair of hydraulic pumps 30, 31 so that the resistive pressure detected by the pressure detector and the actual discharging pressure of the hydraulic pumps 30, 31 detected by the current detector are compared so as to control the motor drive circuit 41 of the pair of hydraulic pumps 30, 31 according to the difference.
According to the seventh feature, in addition to the operation and effect of the fifth feature, that the resistive pressure detected by the pressure detector and the actual discharging pressure of the hydraulic pumps 30, 31 detected by the current detector are compared so as to control the motor drive circuit 41 of the pair of hydraulic pumps 30, 31 in accordance to the difference. Thus the discharging pressures of the hydraulic pumps 30, 31 are quickly corrected to a proper values so as to reduce the resistive pressure acting against the operation of the steering wheel 13 and achieve stabilization quickly.
According to the seventh feature, since the resistive pressure against the steering operation is controlled to increase or decrease according to the difference between the resistive pressure generated by rotation of the helm pump 10 and the actual discharging pressure of the hydraulic pumps 30, 31, it is made possible to decrease the resistive pressure against the steering operation more quickly and stabilized at the reduced level.
Other effects including the energy saving and the feeling of manual steering operation are achieved similarly to the case of the fifth feature.
The steering apparatus of the present invention of eighth feature has the constitution of the first feature wherein at least a hydraulic pump 32 capable of discharging only in one direction is provided as the pump means with the hydraulic pump 32 being installed in series in part of the hydraulic circuit 15 that has the construction of the fully closed circuit, and passage switching means is installed between the hydraulic pump 32 and the helm pump 10 so as to switch the passage amid said hydraulic circuit 15 according to the direction of discharging the liquid from the helm pump 10 and direct the liquid discharged by the helm pump 10 into a suction port of the hydraulic pump 32 regardless of the direction in which the helm pump discharges the liquid, so that discharging pressure is applied in the same direction as the discharging direction of the liquid from the helm pump 10, by means of the pump means that includes the hydraulic pump 32 and the passage switching means in accordance to the resistive pressure against the operation of the steering wheel 13, thereby to reduce the resistive pressure against the operation of the steering wheel 13 automatically.
According to the eighth feature, in addition to the operation and effect of the first feature, when the liquid is discharged from the helm pump 10 in either direction, forward or reverse, by the operation of the steering wheel 13, the passage switching means works in accordance to the direction in which the liquid is discharged from the helm pump 10 and switches the passage of the hydraulic circuit 15 so that the liquid discharged from the helm pump 10 flows into the suction port of the hydraulic pump 32. Therefore, the liquid always flows through the passage switching means installed in the hydraulic circuit 15 into the suction port of the hydraulic pump 32, regardless of the direction in which the liquid is discharged from the helm pump 10. The liquid is further discharged and enters one chamber of the cylinder 20 via the hydraulic circuit 15. As the piston 21 moves, the same amount of liquid is discharged from the other chamber of the cylinder 20 and enters the suction port of the helm pump 10 via the hydraulic circuit 15. Thus use of the passage switching means allows it to use the hydraulic pump 32 capable of discharging only in one direction as the hydraulic pump. Therefore, not only the less expensive hydraulic pump can be used, control mechanism of the pump means can also be made simpler and less expensive.
The energy saving effect and the effect of giving the feeling of manual steering operation can be achieved similarly to the case of the first feature.
According to the ninth feature of the steering apparatus of the present invention, in addition to the constitution of the eighth feature, the pump means that generates the discharging pressure in the same direction as the discharging direction of the helm pump 10 has a pressure detector that detects the resistive pressure generated by rotation of the helm pump 10, while the motor drive circuit 41 that drives the hydraulic pump 32 is controlled so as to generate a discharge pressure that corresponds to the resistive pressure of the liquid detected by the pressure detector.
According to the ninth feature, in addition to the operation and effect of the eighth feature and similarly to the operation and effect of the third and sixth features, the steering wheel can be operated lightly and easily by controlling the hydraulic pump 32 in accordance to the resistive pressure generated by rotation of the helm pump 10.
The steering apparatus of the present invention of tenth feature has the constitution of the eighth feature wherein the pump means, that generates the discharging pressure in the same direction as the discharging direction of the helm pump 10, has a pressure detector that detects the resistive pressure generated by rotation of the helm pump 10 and a current detector that detects the motor current of the hydraulic pump 32, so that the resistive pressure detected by the pressure detector and the actual discharging pressure of the hydraulic pump 32 detected by the current detector are compared and a motor drive circuit 41 of the hydraulic pump 32 is controlled according to the difference.
According to the tenth feature, in addition to the operation and effect of the eighth feature and similarly to the operation and effect of the fourth and seventh features, since the resistive pressure against the steering operation is controlled to increase or decrease according to the difference between the resistive pressure generated by rotation of the helm pump 10 and the actual discharging pressure of the hydraulic pumps 30, 31, it is made possible to decrease the resistance against the steering operation more quickly and stabilized at the reduced level.
The steering apparatus of the present invention of eleventh feature has, in addition to the constitution of the first feature, such a constitution having the hydraulic circuit 14 that consists of a pair of hydraulic circuits 14a, 14b installed between and connecting the steering means and the double action cylinder wherein the entire discharging flow rate of the helm pump 10 is introduced into one of the chambers of the cylinder 20 via one of the pair of hydraulic circuits 14a, 14b and the same amount of liquid is discharged from the other chamber of the cylinder 20 to flow through the other one of the pair of hydraulic circuits 14a, 14b into the helm pump 10, with the hydraulic circuit 14 being made in the construction of the fully closed circuit as a whole and the rudder 27 is moved over a distance that corresponds to the amount of liquid introduced into the cylinder 20.
At least the hydraulic pump 32 capable of discharging only in one direction is provided and is installed in series in the pair of hydraulic circuits 14a, 14b of the hydraulic circuit 14 that is formed in the fully closed circuit construction, and a pair of passage switching means is installed between the hydraulic pump 32 and the helm pump 10 and between the hydraulic pump 32 and the cylinder 20 so as to switch the passage amid the hydraulic circuit 14 according to the direction of discharging the liquid from the helm pump 10 thereby to connect the liquid from the helm pump 10 to the suction side of said hydraulic pump 32 regardless of which direction said helm pump 10 discharges, so that discharging pressure is applied in the same discharging direction from the helm pump 10, by means of the pump means that includes the hydraulic pump 32 and the passage switching means in accordance to the resistive pressure against the operation of the steering wheel 13, thereby to reduce the resistive pressure against the operation of the steering wheel 13 automatically.
According to the eleventh feature described above, in addition to the operation and effect of the second feature, use of the pair of passage switching means makes it possible to make the construction of the hydraulic circuit 14 simpler than in the case of the twelfth feature where only one passage switching means is provided, and the passage switching means itself can be of a simple construction thus allowing it to use an inexpensive switching valve available in the market.
The twelfth feature of the steering apparatus of the present invention has the constitution of the eleventh feature described above wherein the pump means, that generates the discharging pressure in the same discharging direction from the helm pump 10, has a pressure detector that detects the resistive pressure generated by rotation of the helm pump 10, so that the motor drive circuit 41 that drives the hydraulic pump 32 is controlled so as to generate discharge pressure that corresponds to the resistive pressure of the liquid detected by the pressure detector.
According to the twelfth feature, in addition to the operation and effect of the eleventh feature, operation and effect similar to those of the third, sixth and ninth features can be achieved.
The steering apparatus of the present invention of thirteenth feature has the constitution of the eleventh feature wherein the pump means, that generates the discharging pressure in the same discharging direction from the helm pump 10, has a pressure detector that detects the resistive pressure generated by rotation of the helm pump 10 and a current detector that detects the motor current of the hydraulic pump 32, so that the resistive pressure detected by the pressure detector and the actual discharging pressure of the hydraulic pump 32 detected by the current detector are compared and the motor drive circuit 41 of the hydraulic pump 32 is controlled according to the difference of these values.
According to the thirteenth feature, in addition to the operation and effect of the eleventh feature, operation and effect similar to those of the fourth, seventh and tenth features can be achieved.
The steering apparatus of the present invention of fourteenth feature has, in addition to the constitution of the first feature, such a constitution having the hydraulic circuit 14 that consists of a pair of hydraulic circuits 14a, 14b installed between and connecting the steering means and the double action cylinder wherein the entire discharging flow rate of the helm pump 10 is introduced into one of the chambers of the cylinder 20 via one of the pair of hydraulic circuits 14a, 14b and the same amount of liquid is discharged from the other chamber of the cylinder 20 to flow through the other one of the pair of hydraulic circuits 14a, 14b into the helm pump 10, with the hydraulic circuit 14 being made in the construction of the fully closed circuit as a whole and the rudder 27 is moved over a distance that corresponds to the amount of liquid introduced into the cylinder 20.
At least a pair of hydraulic pumps 33, 34 capable of discharging only in one direction are provided as the pump means and are installed in series in the pair of hydraulic circuits 14a, 14b of the hydraulic circuit 14 that is formed in the fully closed circuit construction, so that either one of the pair of hydraulic pumps 33, 34 capable of discharging only in one direction is driven according to the direction of liquid discharged from the helm pump 10 by the operation of the steering wheel 13, and discharging pressure is applied in the same discharging direction from the helm pump 10 in correspondence to the resistive pressure generated by the rotation of the helm pump 10 thereby to automatically reduce the steering resistance of the steering wheel 13.
According to the fourteenth feature described above, in addition to the operation and effect of the second feature, cost reduction can be achieved since the hydraulic pump 32 capable of discharging only in one direction can be used as the hydraulic pump, although the hydraulic circuit and control of the pump become somewhat complicated in comparison to the case of the fifth feature that uses a pair of hydraulic pump 30 capable of discharging in both ways. The combination of the hydraulic pump 32 capable of discharging only in one direction and bypassing the pump provides an advantage of being capable of easily adding manual steering function that is useful in the event of pump failure.
The fifteenth feature of the steering apparatus of the present invention has the constitution of the fourteenth feature described above wherein the pump means, that generates the discharging pressure in the same discharging direction from the helm pump 10, has a pressure detector that detects the resistive pressure generated by rotation of the helm pump 10, while the motor drive circuit 41 that drives the hydraulic pumps 33, 34 is controlled so as to generate discharge pressure that corresponds to the resistive pressure of the liquid detected by the pressure detector.
According to the fifteenth feature, in addition to the operation and effect of the fourteenth feature, operation and effect similar to those of the third, sixth and ninth features can be achieved.
The steering apparatus of the present invention of sixteenth feature has the constitution of the fourteenth feature wherein the pump means, that generates the discharging pressure in the same discharging direction from the helm pump 10, has a pressure detector that detects the resistive pressure generated by rotation of the helm pump 10 and a current detector that detects the motor current of the hydraulic pumps 33, 34, so that the resistive pressure detected by the pressure detector and the actual discharging pressures of the hydraulic pumps 33, 34 detected by the current detector are compared and the motor drive circuit 41 of the hydraulic pumps 33, 34 is controlled according to the difference.
According to the sixteenth feature, in addition to the operation and effect of the fourteenth feature, operation and effect similar to those of the fourth, seventh and tenth features can be achieved.